Expanded List of Themes - Super Light Theme
There are a few more "contrib" themes which aren't included with official releases, but are bundled with development versions/daily builds. You can also download them individually here. Currently "white sky" is the only really light theme I'm aware of there.



Beyond those, there are plenty floating around on blenderartists among others.



To install a theme, drop it in $BLEND_DIR/scripts/presets/interface_theme where $BLEND_DIR depends on your platform and how you installed Blender.